Design of the Accelerating Structures for FMIT

Design considerations and concepts are presented for the accelerating structures for the Fusion Materials Irradiation Test (FMIT) Facility. These structures consist of three major units: a 0.1- to 2-MeV radio-frequency quadrupole based on the Russian concept, a 2- to 35-MeV drift-tube linac made up of two separate tanks designed to generate either 20- or 35-MeV beams, and an energy dispersion cavity capable of spreading the energy of the beam slightly to ease thermal loading in the target. Because of probable beam activation, the drift-tube linac is designed so that alignment and maintenance do not require manned entry into the tanks. This conservatism also led to the choice of a conventional vacuum system and has influenced the choice of many of the rf interface components. The high-powered FMIT machine is very heavily beam loaded and delivers a 100-mA continuous duty deuteron beam to a flowing liquid lithium target. The power on target is 3.5 MW deposited in a 1 × 3 cm spot. Because of the critical importance of the low energy section of this accelerator on beam spill in the machine, a 5-MeV prototype will be constructed and tested at the Los Alamos Scientific Laboratory (LASL).